association list bug? -- version 1.6.4

[Jon Wilson]

Hi y'all,
The following doesn't seem correct.
We have an association list defined such that:

(assoc '+ forms)
=>
(+ . "+")

But,

(assoc-ref '+ forms)
=>
#f

However, if we look at how assoc-ref is supposed to be defined 
according to the guile manual 
("http://www.gnu.org/software/guile/docs/guile-ref/Retrieving-Alist-Entries.html#Retrieving%20Alist%20Entries";), 
we have

(let ((ent (assoc '+ forms)))
    (and ent (cdr ent)))
=>
"+"

Is this a known bug with 1.6.4 and I just need to get off my duff and 
upgrade?

What more information could I provide that might help diagnose this?
Regards,
Jon